Normal tissue homeostasis is a highly regulated process of cell proliferation and cell death. An imbalance of either cell proliferation or cell death can develop into a cancerous state (Solyanik et al., 1995; Stokke et al., 1997; Mumby and Walter, 1991; Natoli et al., 1998; Magi-Galluzzi et al., 1998). For example, cervical, kidney, lung, pancreatic, colorectal, and brain cancer are just a few examples of the many cancers that can result (Erlandsson, 1998; Kolmel, 1998; Mangray and King, 1998; Mougin et al., 1998). In fact, the occurrence of cancer is so high that over 500,000 deaths per year are attributed to cancer in the United States alone.
The maintenance of cell proliferation and cell death is at least partially regulated by proto-oncogenes and tumor suppressors. A proto-oncogene or tumor suppressor can encode proteins that induce cellular proliferation (e.g., sis, erbB, src, ras and myc), proteins that inhibit cellular proliferation (e.g., Rb, p16, p19, p21, p53, NF1 and WT1) or proteins that regulate programmed cell death (e.g., bcl-2) (Ochi et al., 1998; Johnson and Hamdy, 1998; Liebermann et al., 1998). However, genetic rearrangements or mutations of these proto-oncogenes and tumor suppressors result in the conversion of a proto-oncogene into a potent cancer-causing oncogene or of a tumor suppressor into an inactive polypeptide. Often, a single point mutation is enough to achieve the transformation. For example, a point mutation in the p53 tumor suppressor protein results in the complete loss of wild-type p53 function (Vogelstein and Kinzler, 1992).
Currently, there are few effective options for the treatment of many common cancer types. The course of treatment for a given individual depends on the diagnosis, the stage to which the disease has developed and factors such as age, sex, and general health of the patient. The most conventional options of cancer treatment are surgery, radiation therapy and chemotherapy. Surgery plays a central role in the diagnosis and treatment of cancer. Typically, a surgical approach is required for biopsy and to remove cancerous growth. However, if the cancer has metastasized and is widespread, surgery is unlikely to result in a cure and an alternate approach must be taken.
Radiation therapy and chemotherapy are the most common alternatives to surgical treatment of cancer (Mayer, 1998; Ohara, 1998; Ho et al., 1998). Radiation therapy involves a precise aiming of high energy radiation to destroy cancer cells and much like surgery, is mainly effective in the treatment of non-metastasized, localized cancer cells. Side effects of radiation therapy include skin irritation, difficulty swallowing, dry mouth, nausea, diarrhea, hair loss, and loss of energy (Curran, 1998; Brizel, 1998). Chemotherapy, the treatment of cancer with anti-cancer drugs, is another mode of cancer therapy, and most chemotherapy approaches include the combination of more than one anti-cancer drug, which has proven to increase the response rate of a wide variety of cancers (U.S. Pat. Nos. 5,824,348; 5,633,016 and 5,798,339, incorporated herein by reference). However, a major side effect of chemotherapy drugs is that they also affect normal tissue cells, with the cells most likely to be affected being those that divide rapidly in some cases (e.g., bone marrow, gastrointestinal tract, reproductive system and hair follicles). Other toxic side effects of chemotherapy drugs can include sores in the mouth, difficulty swallowing, dry mouth, nausea, diarrhea, vomiting, fatigue, bleeding, hair loss, and infection.
Immunotherapy, a rapidly evolving area in cancer research, is yet another option for the treatment of certain types of cancers. Theoretically, the immune system may be stimulated to identify tumor cells as being foreign and targets them for destruction. Unfortunately, the response typically is not sufficient to prevent most tumor growth. However, recently there has been a focus in the area of immunotherapy to develop methods that augment or supplement the natural defense mechanism of the immune system. Examples of immunotherapies currently under investigation or in use are immune adjuvants (e.g., Mycobacterium bovis, Plasmodium falciparum, dinitrochlorobenzene and aromatic compounds) (U.S. Pat. Nos. 5,801,005 and 5,739,169; Hui and Hashimoto, 1998; Christodoulides et al., 1998), cytokine therapy (e.g., interferons (IL-1, GM-CSF and TNF) (Bukowski et al., 1998; Davidson et al., 1998; Hellstrand et al., 1998), and gene therapy (e.g., TNF, IL-1, IL-2, p53) (Qin et al., 1998; Austin-Ward and Villaseca, 1998; U.S. Pat. Nos. 5,830,880 and 5,846,945) and monoclonal antibodies (e.g., anti-ganglioside GM2, anti-HER-2, anti-p185) (Pietras et al., 1998; Hanibuchi et al., 1998; U.S. Pat. No. 5,824,311). Such methods, while showing some promise, have demonstrated limited success.
Replication-selective oncolytic viruses hold promise for the treatment of cancer (Kim et al., 2001). These viruses can cause tumor cell death through direct replication-dependent and/or viral gene expression-dependent oncolytic effects (Kim et al., 2001). In addition, viruses are able to enhance the induction of cell-mediated antitumoral immunity within the host (Todo et al., 2001; Sinkovics et al., 2000). These viruses also can be engineered to expressed therapeutic transgenes within the tumor to enhance antitumoral efficacy (Hermiston, 2000).
However, major limitations exist to this therapeutic approach. Although a degree of natural tumor-selectivity can be demonstrated for some virus species, new approaches are still needed to engineer and/or enhance tumor-selectivity for oncolytic viruses in order to maximize safety. This selectivity will become particularly important when intravenous administration is used, and when potentially toxic therapeutic genes are added to these viruses to enhance antitumoral potency; gene expression will need to be tightly limited in normal tissues. In addition, increased antitumoral potency through additional mechanisms such as induction of antitumoral immunity or targeting of the tumor-associated vasculature is highly desirable
Therefore, more effective and less toxic therapies for the treatment of cancer are needed. The use of oncolytic viruses presents a potential area for development, however, the limitations discussed above need to be overcome. The present invention addresses these limitations.